Method for manufacturing alloy wheel for automobile

ABSTRACT

A method for manufacturing an alloy wheel for automobiles, the alloy wheel including a rim part having a portion running in and out from a rim flange to a drop center, and a disc part fitted in the rim part is disclosed. The method comprising forging of an alloy billet to obtain a cup-shaped preform, flowforming of the preform to obtain a seamless tube, cutting of the seamless tube into unit tubes, primary roll forming of the unit tube to obtain a preliminarily shaped unit tube, secondary roll forming of the preliminarily shaped unit to obtain a final shaped rim part, and attaching a disc part to the rim part.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for manufacturing an alloy wheel for an automobile, and more particularly to a method for manufacturing an automotive alloy wheel comprising a rim and a disc fitted in the rim.

[0003] 2. Description of the Prior Art

[0004] In general, in manufacturing an alloy wheel for an automobile, it is required to use aluminum or aluminum alloy of high strength and light weight and to afford a fine structure to the whole alloy wheel. In the light of this, it will be appreciated that a rim (or a drum) is a very important part in manufacturing an alloy wheel for an automobile.

[0005] The conventional methods for a conventional alloy wheel can be classified into two types, a liquid metal forging method of forging molten metal into a rim and disc complex, and a continuous forging method of forging a disc type blank continuously. However, the liquid forging method has disadvantages in that the method requires a complex liquid metal forging machine and a complicated process and it is difficult to determine a thickness of a rim for achieving an optimal strength and weight reduction. On the other hand, the continuous forging method has disadvantages in that a procedure for preparing a disc type blank material involves a large loss of raw material and a process for forging the disc type blank into a tube-shaped rim is considerably complicated.

[0006] In general, a forward and backward extrusion process is used for production of an alloy wheel rim from an aluminum tube. However, a large-sized pressing machine must be used to produce large tubes having an outer diameter of 400˜700 mm and a thickness of 3.5˜4.5 mm, and production cost is increased due to poor yield, thereby deteriorating economic efficiency. There is a process of forming a plate material by a deep drawing process, rather than the forward and backward extrusion process. However, the process is deteriorated in economic efficiency because of high price of plate and a large amount of loss of plates. In addition to the above processes, though there is a process of rolling a plate into a cylindrical form and subjecting the cylindrical form to an arc welding process, the process involves problems such as strength reduction of products owing to defects of weld zones, and air leakage from finally produced alloy wheels.

[0007] In a process for forming an aluminum tube according to a shape of a rim of an automotive alloy wheel, a spinning technique is predominantly used. The spinning technique is carried out in such a way that an aluminum tube is shaped by being worked with two or more small rollers passing over the tube while being rotated together with a mandrel. Therefore, the productivity rate of wheels depends on forward speed of rollers advancing along a full width of a rim while working the rim. Since the forward speed is determined in consideration of deformation rate of a workpiece, the working speed usually becomes slow. Moreover, since movement of a roller must be controlled in a radial direction and a longitudinal direction of a tube, a control device is required and it is complicated to set a working condition of wheels.

[0008] Where a disc part is separately prepared and welded to a rim of an automotive alloy wheel, a TIG welding process or MIG welding process is mainly employed in terms of economic efficiency. The welding process involves change of dimensions of welded articles and deterioration of working efficiency due to high heat generated during the welding process, and the welded articles may have defects after the welding process. Consequently, to apply the welding process to production of an alloy wheel, additional weight is required in terms of safety factor, and a correcting operation for deformations of welded articles after a welding process is required. Hence, the above process is required to be improved in terms of productivity and production cost because of its slow working speed.

SUMMARY OF THE INVENTION

[0009] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method for manufacturing an alloy wheel for automobiles including a rim part having a portion running in and out from a rim flange to a drop center, and a disc part fitted in the rim part.

[0010] It is another object of the present invention to provide a method for manufacturing an alloy wheel for automobiles which is intended to remarkably reduce the number of process steps and simplify manufacturing instruments, thereby improving productivity and yield as compared with other methods.

[0011] It is still another object of the present invention to provide a method for manufacturing an alloy wheel for automobiles which is intended to produce a seamless tube having an optimal thickness and high strength and quality by a flowforming process employing flow ability of a metal structure of the tube.

[0012] It is a further object of the present invention to provide a method for manufacturing an alloy wheel for automobiles which allows a rim part to be subjected to a roll forming process at a high speed by rollers having a narrow range of control.

[0013] It is a further object of the present invention to provide a method for manufacturing an alloy wheel for automobiles which is intended to weld a disc part to a rim part without a distortion of shape and necessity for a correction operation.

[0014] In order to accomplish the above object, the present invention provides a method for manufacturing an alloy wheel for automobiles, comprising the following steps: carrying out forging of an alloy billet to obtain a cup-shaped preform; carrying out flowforming of the preform to obtain a seamless tube; cutting the seamless tube into unit tubes; carrying out primary roll forming of the unit tube to obtain a preliminarily shaped unit tube; carrying out secondary roll forming of the preliminarily shaped unit tube to obtain a final shaped rim part; and attaching a disc part to the rim part.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0016]FIG. 1 is a schematic view showing a process for manufacturing an automotive alloy wheel according to the present invention;

[0017]FIG. 2 is a cross-sectional view of an automotive alloy wheel manufactured by a method according to the present invention;

[0018]FIG. 3 is a view showing a process for manufacturing an automotive alloy wheel according to the present invention;

[0019]FIG. 4 is a view showing a process for forging a continuous cast billet into a preform;

[0020]FIG. 5 is a view showing a flowforming process for forming the preform into a seamless tube;

[0021]FIGS. 6 and 7 are views showing a roll forming process for forming a rim part; and

[0022]FIG. 8 is a cross-sectional view showing a finished automotive alloy wheel in which a disc part is welded to a rim part.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.

[0024] Referring to FIG. 2, there is shown an automotive alloy wheel manufactured by a method according to the present invention. As shown in the drawing, the alloy wheel comprises a rim part 16 having a portion running in and out from a rim flange to a drop center, and a disc part 18 fitted in the rim part 16. To produce such an automotive alloy wheel, the rim part 16 is first manufactured, and the disc part 18 is separately welded to the rim part 16. This serial processing steps are shown in FIG. 1.

[0025] The method for manufacturing the rim part 16 comprises a process for preparing a seamless tube as a preliminary product to be formed into the rim part 16 and a process for forming the seamless tube into the rim part 16 with desired shape by a rolling working. A process for preparing a seamless tube, a process of forming the seamless tube into a rim pat 16 with desired shape, and a process for welding a disc part to the rim part is now described in detail.

[0026] [A Process for Preparing a Seamless Tube]

[0027] The method for manufacturing an automotive alloy wheel according to the present invention begins with the preparation of a tube for a flowforming process. Ultimately, this tube is a seamless tube 20 (see FIG. 3b) as a semi-finished product to be worked into a rim part 16.

[0028] First, a continuous cast billet is cut by a circular saw machine and then heated to a forging temperature in a low-frequency induction furnace. Then, the heated metal piece is left in a soaking furnace to achieve a uniform forging temperature. The heated metal piece is subjected to a forging procedure by means of a forging press machine 26 comprising a forging die 22 and a punch 24 (see FIG. 4). More specifically, a lubricant is applied on the forging die 22 and the punch 24, and the heated metal piece is loaded in the forging die 22. Subsequently, hydraulic pressure of the forging press machine is controlled to an appropriate pressure, and the metal piece is subjected to a first offset forging working and a second finishing forging working, thereby obtaining a cup-shaped preform 28, as shown in FIG. 3a.

[0029] By the above forging processes, the preform 28 has a diameter most suitable to be shaped into a rim part 16 and a dimension suitable to be formed into a seamless tube 20 having a thickness of 3.5˜4.5 mm. The preform 28 is precisely formed into a seamless tube 20 by a flowforming machine. The flowforming machine used in this step is shown in FIG. 5.

[0030] The flowforming machine for forming the seamless tube 20 comprises a mandrel 32 around which the preform 28 is fitted, a tail stock coupled to an end of the mandrel 32 for centrally maintaining the mandrel 32, a spindle 35 for turning the mandrel 32 at the other end, an ejector ring for ejecting a forming-finished seamless tube 20 from the mandrel 32, and three rollers 38 (only two rollers are shown in FIG. 5) disposed around the mandrel 32 at an angular interval of 120, but not disposed on a same circumference, which are intended to roll the preform longitudinally. FIG. 5 shows a seamless tube 20 which is almost finished in the flowforming.

[0031] Specifically, the preform 28 is previously applied with lubricant and fitted around the mandrel 32. The preform 28 is radially rolled by the rollers 38 while the mandrel 32 is rotated. During the rolling working, the rollers 38 are forwardly moved along the mandrel 32 at an appropriate speed, thereby allowing thickness of the preform 28 to be reduced by different decrements at several cicumferential locations throughout its length. Since the flowforming process is adapted to reduce thickness of the preform 28 by three rollers disposed at different locations, the process is economical as compared with a conventional process which is carried out three times by one roller.

[0032] By applying the flowforming process as described above to a production of a two-piece type rim which is a model for lightening an automotive alloy wheel, the production cost of an alloy wheel can be remarkably reduced and a seamless tube of high strength and quality, as compared with a conventional forged alloy wheel, can be produced.

[0033] In particular, since an internal diameter of a seamless tube 20 is determined by an external diameter of a mandrel 32 of a flowforming machine 30, thickness of the seamless tube can be changed by only positioning of rollers 38 in case of forming seamless tubes of the same internal diameter.

[0034] Since a seamless tube manufactured by a flowforming process has fine grains and fine surface roughness, its mechanical properties such as tensile strength and elongation are excellent (AA6061-T6 specimen, tensile strength: 32 kgf/mm2, elongation: 12% or more). Since a seamless tube 20 manufactured by the present invention has dimensional accuracy of its external and internal diameters taking into account a equipment tolerance and a roller tolerance, the seamless tube is more superior dimensional accuracy than a conventional process for manufacturing large-sized tubes having a diameter of 400˜700 mm, and has a dimensional accuracy of 0.05˜0.1 mm for an external diameter.

[0035] [A Process for Forming a Rim Part]

[0036] The seamless tube 20 obtained by the above process is cut into tube pieces of a unit length suitable to be shaped into rim parts 16. The cut tube pieces are formed into rim parts 16 by a roll forming machine. The roll forming machine 40 used in this process is shown in FIGS. 6 and 7.

[0037] The roll forming machine 40 comprises a spindle 42, a mandrel 44 fixed to the spindle 42 at its end and having an outer contour corresponding that of a rim part to be formed, a tail stock 46 supporting the other end of the mandrel 44, and first and second rollers 48 and 50 for forming the tube piece into a rim part. The first roller 48 can move only in the radial direction of the work piece while the second roller 50 can move not only in the axial direction of the work piece but also in the radial direction of the work piece.

[0038] As mentioned above, the seamless tube 20 is cut into tube pieces of a unit length suitable to be shaped into rim parts 16 (FIG. 3b). The cut tube unit 21 is fitted around the mandrel 44 fixed to the spindle 42 of the roll forming machine 40 and is stably supported by the tail stock 46. Thereafter, the first roller 48 moves toward the tube unit 21 while the spindle 42 is rotated, so that the tube unit 21 is preliminarily formed into a preformed tube unit 21′ of approximately the shape of the final rim part 16. The reason why the tube unit 21 is preliminarily formed into the preformed tube unit 21′ is that the tube unit 21 may be cracked or may have internal defects due to excessive strain beyond its plastic deformation limit when the tube unit 21 is directly formed into the final shape of the rim part by the first roller 48. As such, the first roller 48 preliminarily moves in the radial direction of the tube unit to form the tube unit into a preformed tube unit 21 having a modest deformation amount, thereby allowing the tube unit to be uniformly worked when being subjected to the final rolling step.

[0039] After the unit tube 21 is preliminarily formed into a preformed tube unit 21′ by the first roller 48, the first roller 48 is retracted, and at the same time the second roller 50 is moved toward the preformed tube unit 21′. As mentioned above, since the second roller 50 is able to move axially and radially with respect to the preformed tube unit 21′, the preformed tube unit 21′ having a gently deformed profile can be formed into a rim part 16 having a portion running in and out from a rim flange to a drop center.

[0040] [A Process for Welding a Disc Part to the Rim Part]

[0041] A disc part 18, which is separately manufactured by a conventional method, is attached to the final formed rim part 16 by a welding operation. In this embodiment, the disc part 18 is welded to the rim part 16 by a laser welding technique. Such a laser welding technique can be substituted with an existing TIG welding or MIG welding. When carrying out the laser welding process, metal articles to be welded are locally and quickly heated, and a time period required to finish the welding process is reduced. Since a welded area is quickly cooled, there is no distortion after a welding process. In particular, welding strength is superior to the above-mentioned existing TIG or MIG welding techniques. In addition, since welded articles have few defects such as blow holes, strengths of welded articles are improved.

[0042] The disc part 18 is attached to the rim part 16 by shrink fitting, and the fitted parts 16 and 18 are transferred to a welding jig where the contact area between the disc part and the rim part is welded by a laser welding machine of 6 kW which moves along the periphery of the disc 18 in a short time.

[0043] By carrying out the welding process of the rim part 16 and the disc part 18 with a laser welding process, time required for welding is shortened, there is no distortion of a wheel due to localized heating, and an additional correction operation is not necessary. Moreover, since there are no defects such as blow holes caused by a TIG or MIG welding process, a welded article has excellent strength. In addition, welded articles are reduced in weight. Furthermore, since a peripheral welding area of a disc having a diameter of 450 mm can be welded within 30 seconds in case of an alloy wheel of 17 inches, productivity is considerably enhanced.

[0044] As described above, the present invention provides a method for manufacturing an automotive alloy wheel which is intended to remarkably reduce the number of process steps and simplify manufacturing instruments, thereby improving productivity and yield as compared with other methods. In particular, since the method according to the present invention produces a seamless tube by a flowforming process utilizing flow ability of a metal structure of the tube, a diameter and a thickness of a tube can be selectively controlled and high strength and quality can be achieved. Also, since a rim part is subjected to a roll forming process at a high speed by rollers having a narrow range of control, it is possible to achieve improved productivity and a significant reduction of fraction defective. The present invention has further advantages in that there is no distortion and no necessity for a correction operation, since a disc fitted in a rim is welded by a laser welding process.

[0045] In addition to the above advantages, the method for manufacturing an automotive alloy wheel according to the present invention has advantages in that, since the method according to the present invention uses flowforming cast billet as starting materials, amount of scraps can be significantly reduced, and is considerably advantageous in terms of raw material cost as compared with conventional methods using plate-shaped materials or disc-shaped materials.

[0046] Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

What is claimed is:
 1. A method for manufacturing an alloy wheel for automobiles including a rim part having a portion running in and out from a rim flange to a drop center, and a disc part fitted in the rim part, comprising the steps of: carrying out forging of an alloy billet to obtain a cup-shaped preform; carrying out flowforming of the preform to obtain a seamless tube; cutting the seamless tube into unit tubes; carrying out primary roll forming of the unit tube to obtain a preliminarily shaped unit tube; carrying out secondary roll forming of the preliminarily shaped unit tube to obtain a final shaped rim part; and attaching a disc part to the rim part.
 2. The method as set forth in claim 1, in which the step of forging the alloy billet includes the steps of cutting a continuous cast billet, heating the cut billet to a uniform forging temperature, carrying out primary offset forging of the heated billet, and carrying out finishing forging of the billet.
 3. The method as set forth in claim 1, in which the flowforming step includes the steps of fitting the preform on a mandrel and rotating the mandrel, and radially and axially moving three rollers disposed around the mandrel at an angular interval of 120, but not disposed at a same circumferential line at a predetermined speed, to roll the preform throughout its length, thereby causing the preform to be continuously reduced in thickness.
 4. The method as set forth in claim 1, in which the primary roll forming step includes moving a first roller of a roll forming machine in a radial direction of the unit tube to obtain the preliminarily shaped unit tube and then retract the first roller, and the secondary roll forming step includes moving a second roller of a roll forming machine in radial and axial directions of unit tube to obtain the final shaped rim part.
 5. The method as set forth in claim 1, in which the step of attaching the disc part to the rim part includes fitting the disc part into the rim part by shrink fitting and carrying out a laser welding of the disc and rim parts held in a welding jig. 